<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        /* 
         需求分析：
           1.提示用户输入一个值
           2.判断，如果小于10，则补零

        */
       let num = prompt('请输入一个数');
       
       num = num.length < 2 ? '0' + num : num ;
       console.log(num);
    </script>
</body>
</html>